Sivakov is surely an exceptional rider. He had been the youngest rider to finish in the top10 of a GT in many years at the Giro before Pogacar beat him in that statistics at the Vuelta. He's had an exceptional season. He totally deserves to be considered a future GT winner.
It's just that we've recently got many freaks of nature in road cycling. Bernal, Pogacar, Evenepoel and Van der Poel. It feels like we should only get one rider like that per every 5-10 years but they've all emerged within 2 years. It makes a rider like Sivakov to look less impressive by comparison but he could have easily been hailed as the greatest talent of his generation had he been born a couple of years earlier. He might not been the most impressive young rider of his generation but for me he is still among few most impressive young riders among a longer span of time and he makes the cut as a probable GT winner in the future. He might not be likely to turn better than Bernal, Evenepoel and Pogacar but I find it pretty likely that he will turn better than the generation that came just before them and will come after them, therefore making Sivakov a likely candidate to win a GT that will not be contested by any of these 3 riders in their top shape. There's also a possibility that at least one of these 3 will share the fate of riders like Andy Schleck or Nairo Quintana and will not keep delivering results everyone expected from them after their mid 20-ties, making even more room for Sivakov to win something big at some point.